xkcd

New (economically) type of FTL travel

New (economically) type of FTL travel

Posted: Thu Mar 10, 2016 5:20 pm UTC

by Quizatzhaderac

This idea is strictly a "hey wouldn't this be interesting" thing, not a "remotely possible" or even a "I"d want to live in this universe" thing. (In fact I'd suggest the universes we don't want to live in tend to be the most interesting!)

Description:

Users of a space ship pick any target point in the universe. Each ship has a accuracy parameter (usually between 1.5 and 4, unitless of type distance per distance).

Travel between the source point and the actual destination is instantaneous. Specifically the traveler experiences zero/trivial time traveling and arrives at their destination either a moment later in their original time frame, or a moment later than they would need to cause a time paradox. Fuel consumption, ship wear, et cetra is independent of distance.

The actual destination is not always the target destination, in fact the probability of that is vanishingly small at long distances.

The actual destination is always a random point in orbit around a star (Or more generally somewhere as opposed to the vast amounts of nowhere empty space provides). The reasons for this are handwavey; maybe something like you need to come out at the right gravitational potential. STL engines are good enough to get from this random point to places of interest in the system.

The actual destination statistics are determined thusly: The distance between the origin and target point is divided by the accuracy parameter. That number becomes the lamda in a simple exponential distribution. That distribution describes the distance from the target. The direction of the error is uniform in all directions. The resulting point follows gravity to the nearest star.

Observing a ship jump can tell you a ship's desired destination, but not how the random part resolved.

Implications:

Most generally: it's easy to get somewhere interesting; it's hard to get to the planned spot. The character wants to go to the planet of green skinned women; the author wants the character to go to the planet of planet of having-to-fight-death-matches-against-your-friends. If interstellar travel is too hard and the whole story is the lives of the descendants 1% of the way through the trip; if it is too easy and the characters just go to the green planet.

People determined to go to a specific location would make a series of jumps targeting their desired destination each time and on average cutting the distance to a fraction, with the small rounding down effect prevents Xeno's paradox. The intermediate points would be uncontrollable. Ending up further than you started is possible, but somewhat uncommon.

The relative locations of stars matter, in that one must be concerned with where they might accidentally end up. Negatively: they'd want to avoid dangerous locations. Positively: the quantity and quality of next best locations would be a boon.

Particularly bad failures would be ending up much further than you started or running out of fuel (or running low to the point of desperation).

Registration of ships (aka reputation management systems) would be very important so one could know that their uber driver isn't Sweeny Todding them.

Ships not wanting to be found/followed could deliberately reduce their accuracy to .1 and target the next star. This maneuver (I'll call it a dodge, but as an evasion and a "get out of Dodge") would result in less than a 1 in 20 chance of being at the target (or any specific star) and require searching about 444 stars to get a 50% chance of finding them.

Trade for fungible goods would be conducted by determining the average price of good based off a target destination with buying and selling plans readjusted for the facts of each jump.

Email would be marked with a recipient and some distribution of potential locations. As ships travel they would propagate copies of the email until hopefully it is received. Cleaning up these copies would be technically complicated, but I assume it could be done in a secure and reasonably efficient way.

Travelers and parcel post could be done in some cases with ships determined to reach specific locations, but it's be more economical to switch between a series of ships heading in the right general direction.

-editExamples of mathA jump from sol to Alpha Centuari with the worst type of engines (1.5) would have a 77.7% chance of actually arriving there, a 17.3% chance of arriving at one of Centuri's immediate neighbors, a 3.8% chance of arriving two stars away, et cetra.

Travelers would indeed have a preference for more reliable routes, but this would need to be a trade off with time and fuel economy. If one wanted to get to Rigel (860 ly) one would need to make 215 such jumps successfully versus (or more like 280 with failures).It would take typically 12 jumps shooting straight at Rigel the whole time.

Re: New (economically) type of FTL travel

Posted: Thu Mar 10, 2016 6:54 pm UTC

by Xanthir

Standard IP can take care of email, I think. It routes along corridors likely to be faster, but can travel in multiple directions if necessary, and can be dedup'd along the way. You'd have to tune it a bit for the extreme high latency, of course.

Re: New (economically) type of FTL travel

Posted: Fri Mar 11, 2016 5:50 pm UTC

by PM 2Ring

I like it!

Quizatzhaderac wrote:Each ship has a accuracy parameter (usually between 1.5 and 4, unitless of type distance per distance).

Travel between the source point and the actual destination is instantaneous. Specifically the traveler experiences zero/trivial time traveling and arrives at their destination either a moment later in their original time frame, or a moment later than they would need to cause a time paradox. Fuel consumption, ship wear, et cetra is independent of distance.

Any trajectory that's FTL can be used to cause a time paradox. So you might want to handwave that away as well.

Quizatzhaderac wrote:The actual destination statistics are determined thusly: The distance between the origin and target point is divided by the accuracy parameter. That number becomes the gamma in a simple exponential distribution. That distribution describes the distance from the target. The direction or the error is uniform in all directions. The resulting point follows gravity to the nearest star.

Observing a ship jump can tell you a ship's desired destination, but not how the random part resolved.

The gamma? Or do you mean the lambda, λ?

A suggestion: make the fuel consumption &/or ship wear a function of the accuracy parameter. I guess a simple linear function, where greater accuracy costs more would be adequate. Or it could be a Gaussian function to discourage people from using a low accuracy parameter too much, but I guess that's not really necessary because over-use of low accuracy has a time penalty.

Re: New (economically) type of FTL travel

Posted: Sat Mar 12, 2016 7:24 am UTC

by stopmadnessnow

PM 2Ring wrote:I like it!

Quizatzhaderac wrote:Each ship has a accuracy parameter (usually between 1.5 and 4, unitless of type distance per distance).

Travel between the source point and the actual destination is instantaneous. Specifically the traveler experiences zero/trivial time traveling and arrives at their destination either a moment later in their original time frame, or a moment later than they would need to cause a time paradox.

Economically (and maybe even socially?) it might be better if they stay on the ship longer and have something like a night club on board? If that's not possible due to the g-force like aggrevation at least keep them in long enough to show a movie, and get a bit of revenue back that way? This instantaneousness may not be an ideal selling pitch.

Also, I like the idea that the pilot might be Sweeney Todding them. Does that mean they turn into the contents of pies as soon as they arrive?

Re: New (economically) type of FTL travel

Posted: Sat Mar 12, 2016 7:27 pm UTC

by Hypnosifl

PM 2Ring wrote:Any trajectory that's FTL can be used to cause a time paradox. So you might want to handwave that away as well.

One way out of this is to posit a preferred reference frame for FTL travel, so regardless of a person's velocity relative to this frame (and how their definition of simultaneity differs from the preferred frame) before jumping to FTL, when they do make the jump they are constrained so that their FTL trajectory must always be forward in time, or possibly instantaneous, relative to this frame (i.e. according to this frame's definition of simultaneity, the event of dropping out of FTL always happens at a time greater than or equal to the time of jumping to FTL).

Re: New (economically) type of FTL travel

Posted: Mon Mar 14, 2016 3:04 pm UTC

by Quizatzhaderac

PM 2Ring wrote:The gamma? Or do you mean the lambda, λ?

Indeed; fixed.

stopmadnessnow wrote:Economically (and maybe even socially?) it might be better if they stay on the ship longer and have something like a night club on board? If that's not possible due to the g-force like aggrevation at least keep them in long enough to show a movie, and get a bit of revenue back that way? This instantaneousness may not be an ideal selling pitch.

I mean purely the FTL portion is instant. I didn't specify travel time within star systems, enpalnning/deplanning, customs, et cetra. I suppose there might also be something like warm up and coll down periods before and after jumping.

Also, I like the idea that the pilot might be Sweeney Todding them. Does that mean they turn into the contents of pies as soon as they arrive?

Yes; or kidnapping them for ransom/slavery, if we want to be more serious; or forcing them to get new haircuts, if we want to be less serious.

Hypnosifl wrote:One way out of this is to posit a preferred reference frame for FTL travel

If you think about it, my condition "arrives at their destination .... a moment later than they would need to cause a time paradox" implies a preferred frame.

Re: New (economically) type of FTL travel

Posted: Tue Mar 15, 2016 2:41 am UTC

by Xanthir

Quizatzhaderac wrote:If you think about it, my condition "arrives at their destination .... a moment later than they would need to cause a time paradox" implies a preferred frame.

Or it implies that this is effectively light-speed.

Re: New (economically) type of FTL travel

Posted: Thu Mar 24, 2016 2:56 pm UTC

by tomandlu

How do you create a time-paradox in this scenario? All the paradoxes I've seen seem to depend on communication between moving ships.

Re: New (economically) type of FTL travel

Posted: Thu Mar 24, 2016 4:02 pm UTC

by Quizatzhaderac

The Tachyon anti-telephone paradox can still be done by passing paper notes, by using FTL ships to send the messages.

Suppose we have two slower -than-light geodesics (paths) V (Venutiandesic) and M (Martialesic) that intercept at some-point (S) in the future.

Alice and Bob are in my-style spaceships and start off at point A1 and B1 on geodesics V and M, respectively. Each of them plans to jump to a point on the other geodesic (A2 and B2), then accelerate to match it and follow it to point S. A1 and B1 are equidistant from S.

I'm too lazy to create an image file, find host and all, so I'll just describe how Alice would graph out her itinerary.

She'd label the vertical axis time, and the horizontal axis space.

She'd draw V as a vertical (no motion, to time dilation) because relativity says you don''t argue with Alice.

She'd draw M at a shallow angle to vertical, because it's moving through space to her.

From A1 she'd draw a horizontal line to represent her teleportation and A2 at the intersection of this new horizontal line and M

She'd get curious about Bob and decide to draw B1. Let's see B1 is the same distance from S as A1, but M isn't vertical, so...?!?! That puts B1 above A1 and A2!

She would draw a line perpendicular to M for Bob's teleportation, which puts B2 below A1.

As a sanity check, she repeats everything from Bob's perspective. They disagree about the timings of A1 vs B1 and A2 vs B2, but they both agree that A1 is after B2 and B1 is after A2.

Re: New (economically) type of FTL travel

TBH, I'm no wiser (I never really understand this concept however it's phrased), so can I ask a simple Y/N question, and then I'll try to figure out the details later?

Q: Using this model, can Alice send a message to herself that she then receives in the past? (i.e. a message with no origin)

Re: New (economically) type of FTL travel

Posted: Fri Mar 25, 2016 8:14 pm UTC

by Quizatzhaderac

Yes, Alice can receive a note at A1,pass it to Bob ad B1,who can then pass it back to Alice at A1 again.

Re: New (economically) type of FTL travel

Posted: Sat Mar 26, 2016 12:28 am UTC

by tomandlu

Quizatzhaderac wrote:Yes, Alice can receive a note at A1,pass it to Bob ad B1,who can then pass it back to Alice at A1 again.

Thanks (sort of - now I've got to figure it out).

Re: New (economically) type of FTL travel

Posted: Fri Apr 01, 2016 10:51 pm UTC

by Hypnosifl

Quizatzhaderac wrote:The Tachyon anti-telephone paradox can still be done by passing paper notes, by using FTL ships to send the messages.

Are you talking about what would happen if there was no preferred frame for FTL travel? I thought you said earlier that you were imagining a preferred frame, which would prevent this sort of paradox.

Re: New (economically) type of FTL travel

Posted: Mon Apr 04, 2016 2:30 pm UTC

by Quizatzhaderac

Yes, I was explaining to Tomandlu what would happen without a preferred frame, because he expressed confusion about the available paradoxes.

And yes, my made up rules have a preferred frame. The anti-telephone paradox is an off topic.

Re: New (economically) type of FTL travel

Posted: Wed Apr 20, 2016 10:27 pm UTC

by DanD

How do you deal with the situation where there is only one viable star in the error range of the jump.

As stated, the potential error of the jump is 1+/-0.6 for the worst class of ships. Unless I'm mistaken, a jump in the direction of the Centaurii system, from earth lands you at one of the Centaurii stars, there are no other stars in the neighborhood. This isn't perfect, but the reverse jump always lands you back at earth. Likewise, Sol to Struve or Cygni(I think) always works, because there are no other stars in the vicinity. Definitely for the higher class of ships.

I suspect there would be a strong desire to map out routes that are "certain", either in both directions or as a loop. This may be less efficient than a single jump, if you get lucky, but in many cases would net out better on average, and it eliminates a lot of the uncertainty. A mixed strategy of such routes with randomized jumps for long distances might also be used.

Re: New (economically) type of FTL travel

Posted: Thu Apr 21, 2016 3:55 pm UTC

by Quizatzhaderac

An exponential distribution doesn't have a maximum value. The error of .66 is how far one is off on average, not the max.

It's in fact possible for any jump to take the traveler anywhere in the universe, it's just a matter of how likely one is to end up in a given location.

A jump from sol to Alpha Centuari with the worst type of engines would have a 77.7% chance of actually arriving there, a 17.3% chance of arriving at one of Centuri's immediate neighbors, a 3.8% chance of arriving two stars away, et cetra.

Travelers would indeed have a preference for more reliable routes, but this would need to be a trade off with time and fuel economy. If one wanted to get to Rigel (860 ly) one would need to make 215 such jumps successfully versus (or more like 280 with failures).It would take typically 12 jumps shooting straight at Rigel the whole time.

Re: New (economically) type of FTL travel

Posted: Fri Apr 22, 2016 12:43 pm UTC

by jewish_scientist

Because your system is probabilistic, you could just have that remove all paradoxes. Like, imagine Adam is at point A and would create a paradox if he travels to point B. The probability of him arriving at point B was 99.999999999999999999999999999998%. However when he makes the jump, he does not end up at point B. So he goes back to point A and tries again; still, he does not arrive at point B. He tries again and again, but the jump never goes right. It is as if The Universe has given a bribe to the Law of Truly Big Numbers just to mess with wise-guys trying to make paradoxes.